Substrate processing apparatus and substrate processing method

A substrate processing apparatus includes: a protrusion portion formed by a side peripheral wall of a processing container which swells outward, and configured to form a vertically elongated space communicating with a processing space for accommodating a substrate holder and performing a process; a gas discharge portion provided in the vertically elongated space, and configured to discharge a process gas into the processing space; an antenna provided in the protrusion portion along a vertical direction and supplied with a high-frequency power for converting the process gas into a plasma in the vertically elongated space; and a shield extending leftward and rightward in the protrusion portion at positions closer to the processing space than the antenna and configured to shield an electric field formed by the antenna and to suppress a formation of the plasma in the processing space.